PlatformKeys: Update API and tests OWNERS file

Change-Id: I9ca6ad82d45f396eef304f3337d84cbc0f707b79
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2424317Reviewed-by: Pavol Marko <pmarko@chromium.org>
Reviewed-by: Maksim Ivanov <emaxx@chromium.org>
Commit-Queue: Omar Morsi <omorsi@google.com>
Cr-Commit-Position: refs/heads/master@{#810147}

chrome/browser/chromeos/platform_keys/OWNERS

 emaxx@chromium.org
-pmarko@chromium.org
 omorsi@google.com
+pmarko@chromium.org
 
 # COMPONENT: Enterprise

chrome/browser/extensions/api/platform_keys/OWNERS

 emaxx@chromium.org
+omorsi@google.com
+pmarko@chromium.org
 
 # COMPONENT: Enterprise

chrome/test/data/extensions/api_test/platform_keys/OWNERS

 emaxx@chromium.org
+omorsi@google.com
+pmarko@chromium.org
 
 # COMPONENT: Enterprise